How can I determine what frequency a device is transmitting on?

[Descartes]

For example, I have this communications device in my car that's synced to open/close my garage door. How can I determine what frequency it is using? I have about 3 more buttons in my car that do nothing, and I was wanting to put an RF receiver on my computer to respond to signal and perform some action (turn lights on using X12 protocol over a serial line, perhaps?).

Do I just need a spectrum analyzer to look at the strongest signal nearby? Thanks!

 

[ATLien247]

If there is such a device, I bet it's illegal.

Just imagine all the free stuff... er... I mean theft that could be had...

 

[NutBucket]

Spectrum Analyzer it is.

 

[Ranger]

A spectrum analyzer would be the best way, if you can get one.
A O-Scope would work in a pinch.
What test equipment can you get your hands on?
Andy

 

[crab]

My Icom scanner will analyze a spectrum...

screenie (scanning 110-130MHz)

 

[NutBucket]

Note: Obviously there is more going on then a simple frequency activation, I think.

 

[tweakmm]

you're going to need something on your computer to pick up the signal

 

[Miramonti]

How about a real spectrum analyzer? Or, you could by a car instead.

 

[crab]

Oh yea, you can find the FCC ID and look it up here...

 

[JW310]

I think a handheld frequency counter would work just as well for at least telling you what frequency the transmitter is on.

JW

 

[Heisenberg]

A spectrum analyzer would certainly tell what frequency it operates on, but it's probably printed on the thing or in the manual somewhere. Then you're going to have the problem of making the receiver react to the appropriate signal. The output of the opener is probably some kind of digital signal that sends a certain code. You could have the receiver simply react to any strong enough modulation on that frequency, but then you have the risk of a stray signal setting it off.

 

[Ranger]

Yes you're right, that's why I would like the spectrum analyzer so I could see how the carrier was modulated.
Andy

 

[Desslok]

Pick up a copy of Monitoring Times they have ads for freq. catchers. They are not illeagel.

 

[Descartes]

Thanks for all the replies guys.

I really just want to a) find out what frequency a device is transmitting on, and b) somehow detect the transmission of said signal and operate on it. I know that there will be some ambiguities involved as I can't be certain the signal is coming from the appropriate device without analyzing the sine wave through a spectrum analyzer, but I just want something to play with

I had also wanted a spectrum analyzer capable of 2.4ghz to look for interference when doing 802.11b installs, but I couldn't really find what I needed.

I have a Garmin GPS antenna/receiver that I use to retrieve GPS information. I'd rather like to receive radio signals of a given frequency in the same manner.

Any ideas? I'd like something that communicated over an rs232 (serial) link if possible, but I don't really care how it works. I could try to build my own from some schematics, but I'm not that proficient with the hardware.

So, a frequency counter will give me the frequency, now how do I receive it w/ my software without spending $1200 on a spectrum analyzer?

I think I'm being redundant, so I'll stop rambling. Thanks!

 

[Descartes]

Yes you're right, that's why I would like the spectrum analyzer so I could see how the carrier was modulated.

That would be nice, although in my case the modulation used doesn't really matter as I don't be demulating anything. Most devices I want to try and communicate with probably use their own means of modulation (like how GPS uses the PRC codes, etc.).

Pick up a copy of Monitoring Times they have ads for freq. catchers

I'll check that out. Thanks!